This application claims the benefit of Korean Patent Application No. 10-2004-0075484, filed on Sep. 21, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a polygonal mirror unit for scanning a beam emitted from a light source onto a surface to be scanned, a light scanning unit, and an image forming apparatus employing the same. More particularly, the invention is directed to a polygonal mirror unit constructed to prevent contamination using photocatalyst, a light scanning unit, and an image forming apparatus employing the polygonal mirror and the light scanning unit.
2. Description of the Related Art
In general, a light scanning unit is used in a laser printer, a digital copier, a barcode reader, a facsimile, or the like to produce a latent image on an exposed object through main scanning by a beam deflector and subscanning by rotation of the exposed object.
Referring to FIG. 1, a typical light scanning unit includes a light source 1 that produces and emits a beam, a beam deflector 5 that deflects the beam emitted by the light source 1 to be scanned onto an exposed object 9, and an f-θ lens 7 that corrects an error contained in the beam deflected by the beam deflector 5. In addition, a collimating lens 2 that collects the divergent beam from the light source 1 and a cylindrical lens 3 that shapes the beam are disposed in an optical path between the light source 1 and the beam deflector 5.
The beam deflector 5 includes a driving source 5a and a rotating polygonal mirror 5b rotated by the driving source 5a. Accordingly, a scanning direction is determined depending on the reflection direction of a beam that changes as the polygonal mirror 5b rotates. Thus, when the polygonal mirror 5b rotates clockwise, the beam incident on the polygonal mirror 5b is scanned onto the exposed object 9 in main scanning direction as indicated by an arrow A.
Meanwhile, there is a need to prevent contamination of the polygonal mirror 5b with foreign materials in the light scanning unit configured as described above because the contamination significantly degrades scanning performance.
As a solution to prevent this contamination, Japanese Patent Publication No. hei 5-72495 for A Laser Beam Printer published on Mar. 26, 1993 discloses a cover for preventing contamination on a polygonal mirror. The cover is separately located within an optical box containing a light scanning unit and encloses the polygonal mirror. Through a holder, a glass is fitted into a groove formed in one side of the cover and through which a beam enters and exits. The cover protects the surface of the polygonal mirror from contamination during operation.
However, due to the use of a separate cover for prevention of contamination the manufacturing costs are high, and an assembly manufacturing process is very complicated. While the cover prevents inflow of external air, the possible presence of contaminants in air flowing into the work area during assembling reduces the effect of the cover, and there is a high risk of contamination due to oil that is finely sprayed from a polygonal mirror driving motor. Furthermore, the use of a cover may only retard contamination but cannot completely eliminate the risk of contamination.